A crankcase lubricant is an oil used for general lubrication in an engine where there is an oil sump below the crankshaft of the engine and to which circulated oil returns. It is well known to include additives in crankcase lubricants for several purposes. Friction modifiers, also referred to as friction-reducing agents, may be boundary additives that operate by lowering friction coefficient and hence improve fuel economy; the use of glycerol monoesters as friction modifiers has been described in the art, for example in U.S. Pat. No. 4,495,088; U.S. Pat. No. 4,683,069; EP-A-0 092 946; and WO-A-01/72933. Glycerol monoester friction modifiers have been and are used commercially.
GB-A-2 106 106 describes reducing fuel consumption in an internal combustion engine by lubricating the engine during operation with a lubricating composition comprising a minor amount of at least one ester having the formula R1 (COOR4)m wherein:
R1 is an aliphatic hydrocarbon-based radical free from acetylenic unsaturation and containing from about 10 to about 35 carbon atoms, in which at least 8 carbon atoms are in a straight-chain configuration;
each R4 is independently hydrogen or an alkyl or alkenyl radical containing up to about 18 carbon atoms, at least one R4 being alkyl or alkenyl; and
m is an integer from 2 to 5.
Formulators of lubricants are always seeking further ways of reducing the amount of fuel consumed in operation of internal combustion engines.